It's always best to get an extra roll too as if they sell out of the batch number that you have it is often hard to get another one with that number. A different batch may look the same when it is on the roll but will not be the same when it goes up. You should get 4 per roll for the length you say. Many stores will refund you for any spare rolls you have as long as they are not opened so check that one first as well.